20 November 2010

Australian white sharks in the Mediterranean Sea

Some cetaceans and birds are known to perform long-distance movements. Now, a recent study explains how white sharks could also be added to this ‘record’ list. Researchers found out that white sharks living in the Mediterranean Sea are closely related to those living in Australian waters.

About 450,000 years ago, while some individuals were swimming between Australia and Africa, strong abnormal currents deviated their routes and probably led them to the west coast of Africa. Once there, they would have tried in vain to head east again to go back on their route but ended in the Mediterranean.

"Once they got to the Mediterranean they may have become trapped because its peninsulas and channels make it like a giant lobster pot (…) But because white shark females return to the area where give birth, once they birth in the Mediterranean they become a fixture, shaping and rebalancing the ecosystem" commented Jones, one of the authors.


---Image: ‘Bruce’ the white-shark in the famous cartoon ‘Finding Nemo’.

Gubili C., Bilgin R., Kalkan E., Karhan S.U., Jones C.S., Sims D.W., Kabasakal H., Martin A.P., Noble L.R. 2010. Antipodean white sharks on a Mediterranean walkabout? Historical dispersal leads to genetic discontinuity and an endangered anomalous population. Proceedings of the Royal Society B. 10.1098/rspb.2010.1856

ABSTRACT: The provenance of white sharks (Carcharodon carcharias) in the Mediterranean is both a conundrum and an important conservation issue. Considering this species's propensity for natal philopatry, any evidence that the Mediterranean stock has little or no contemporary immigration from the Atlantic would suggest that it is extraordinarily vulnerable. To address this issue we sequenced the mitochondrial control region of four rare Mediterranean white sharks. Unexpectedly, the juvenile sequences were identical although collected at different locations and times, showing little genetic differentiation from Indo-Pacific lineages, but strong separation from geographically closer Atlantic/western Indian Ocean haplotypes. Historical long-distance dispersal (probably a consequence of navigational error during past climatic oscillations) and potential founder effects are invoked to explain the anomalous relationships of this isolated ‘sink’ population, highlighting the present vulnerability of its nursery grounds.

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